This invention relates to a process for neutralizing acidic catalyst residues remaining in alpha-olefin polymers. More particularly, the present invention relates to an improvement in the deashing process of propylene polymers such as polypropylene.
The polymerization of alpha-olefins, such as propylene alone or with other copolymerizable alpha-olefins, is well known and described in numerous patents, such as U.S. Pat. Nos. 2,112,300, 3,113,115, 3,197,452, Belgian Pat. No. 538,782 and British Pat. No. 994,416.
The catalyst is normally prepared from a transition metal compound, preferably a halide, and a reducing component consisting normally of metallic aluminum or a metal alkyl compound. Representative of the transitional metal compounds used is a metal selected from Groups 4B, 5B, and 6B of the Periodic System.* Included in the preferred species are the titanium halides, for example, titanium tetrachloride, titanium trichloride, and titanium dichloride and mixtures thereof. Other metal compounds, such as zirconium tetrahalide and hafnium tetrachloride, vanadium chloride, chromium chloride, tungsten chloride, and the like, are especially useful. Still other transitional metal halides containing halogens selected from the group consisting of bromine iodine, chlorine, and in certain instances, fluorine, can also be used. FNT *Handbook of Chemistry and Physics, The Chemical Rubber Co., Cleveland, Ohio, 45th Edition, 1964, p. B-2
The reducing component of the catalyst composition may be any of a variety of reducing agents. Most common among the reducing agents are the organometallic compounds such as triethyl aluminum, aluminum diethyl chloride, aluminum ethyl dichloride, aluminum diethyl hydride, aluminum triisobutyl, aluminum triisopropyl, and related compounds. Many other reducing agents such as lithium aluminum hydride, zinc ethyl hydride, and the like are described in the literature as useful reducing agents and can also be used. These catalyst are all of the now well known "Ziegler" variety.
Certain Ziegler catalyst, or more particularly, certain modified Ziegler catalysts, have been found to be especially useful for polymerizing alpha-olefins. For example, a titanium trichloride catalyst modified with aluminum chloride having the formula, 3TiCl.sub.3.AlCl.sub.3. Normally, this modified Ziegler catalyst is activated with a metal alkyl such as an aluminum alkyl, and preferably with an aluminum alkyl halide having the structural formula, R.sub.2 AlX or R.sub.3 Al.sub.2 X.sub.3, wherein R is selected from the group consisting of alkyl radicals containing 1 to 12 carbon atoms or phenyl or benzyl radicals, and X is a halogen atom selected from the group consisting of chlorine, bromine or iodine.
For purposes of this invention, the transitional metal halide and the reducing component are present in molar ratios about 1 to 1. However, molar ratios of the transitional metal halide and the reducing component can be present in mole ratios from as low as 0.1 to 1 to as high as 6 to 1. If TiCl.sub.3 is the transitional metal halide and diethyl aluminum chloride is the reducing agent, an aluminum to titanium ratio of about 0.33 atom of aluminum per atom of titanium is preferably used.
In a typical polymerization, liquid alpha-olefin is contacted with a catalyst such as TiCl.sub.3.1/3AlCl.sub.3 plus diethyl aluminum chloride in about 1 to 2 weight ratio. Productivity typically ranges from about 500 to 3000 pounds of polymer per pound of TiCl.sub.3.1/3AlCl.sub.3 catalyst.
The catalyst is simply prepared by mixing the various components whereupon an active catalyst is formed. If desired, the activated catalyst can be aged or otherwise further treated prior to use. For example, alkali metal halides, such as sodium chloride, potassium iodide, lithium bromide, or sodium fluoride, can be used as additives for improving catalyst efficiency and for controlling the length of the polymer chain.
The preferred catalyst composition for the polymerization of propylene comprises a modified titanium trichloride having the structural formula, 3 TiCl.sub.3. AlCl.sub.3, activated with diethyl aluminum chloride. Ratios of diethyl aluminum chloride and titanium trichloride of between 0.3:1 and 6:1 may be advantageously used. The presence of an alkali metal halide in an amount of between 0.5 to 10 mols of an alkali metal halide per mol of reduced titanium tetrahalide, and preferably a mol ratio of from 0.8 to 5 mols of an alkali metal halide, such as sodium chloride, per mol of reduced titanium tetrahalide can be used for improving catalyst activity.
A variety of monomers may be polymerized with the Ziegler type catalysts. Any unsaturated hydrocarbon corresponding to the general formula, R--CH.dbd.CH.sub.2, wherein R is selected from the group consisting of an alkyl radical having from one to six carbon atoms, a phenyl radical, and an alkyl substituted phenyl radical can be used. Examples of specific unsaturated hydrocarbons which can be polymerized include alpha-olefins containing 3 to 8 carbon atoms, such as propylene, butene, isobutylene, pentene, isoamylene, hexene, isohexenes, heptene, isoheptenes, octene, isooctenes, and the like. Unsaturated hydrocarbons containing 3 to 5 carbon atoms are especially suitable. Diolefins, such as butadiene and isoprene, and alkyl substituted ethylenic compounds having 6 to 8 carbon atoms, such as sytrene, methylstyrene, and the like, may also be polymerized by these processes. Mixtures of any of the above monomers can also be used.
The monomers may be polymerized at moderate temperatures and pressures with the Ziegler type catalysts described above, generally at temperatures of 0.degree. C. to 150.degree. C., with temperatures on the order of 25.degree. C. to 80.degree. C. being particularly useful. A solvent may be employed for the polymerizations, however, the olefin monomer is frequently used for this purpose. The polymerizations are perferably conducted under conditions that exclude atmospheric impurities such as moisture, oxygen and the like.
The pressure ranges from about atmospheric pressure to about several atmospheres with pressures in excess of about 500 psi rarely being employed.
After the polymer has been produced, the catalyst is deactivated by contacting the polymeric reaction mixture with a material which reacts with and deactivates the catalyst. Such materials include, for example, low alcohols, acetone and water. Thereafter, the polymer may be separated from the diluent, washed with water and dried. The removal of residual amounts of catalyst is most important since even the small amounts remaining after water washing can be detrimental to the polymer. Residual ash can be detrimental, for example, during extrusion of the polymer, wherein filter screens may become plugged by the ash or if not filtered from the polymer the ash may cause inherent weaknesses in the product, particularly filaments. Residual ash also may adversely effect antioxidant stability in the polymer and cause poor color qualities. Furthermore, proper neutralization is not normally practical without deashing. An acid polymer is undesirable, for example because of excessive equipment corrosion and poor polymer color properties. As used herein the phrase "neutralize the polymer" is understood to refer to neutralizing the acid components present in admixture with the polymer such as the chloride.
It is an advantage of the present invention that a high degree neutralization of the acidic and potentially acidic catalyst components is obtained. It is a further advantage of the present process that the neutralizing is not detrimental to the deashing. It is a particular feature of the present invention that polymer having excellent deashed and neutral characteristics is produced. These and other features and advantages will become clear from the following discussion.